In the United States a standard has been proposed for digitally encoded high definition television signals. This standard is essentially the same as the MPEG-2 standard, proposed by the Moving Picture Experts Group (MPEG) of the International Standards Organization (ISO). The MPEG-2 standard is described in an International Standard (IS) publication entitled, "Information Technology--Generic Coding of Moving Pictures and Associated Audio, Recommendation H.626", ISO/IEC 13818-2, IS, 11/94 which is available from the ISO and which is hereby incorporated by reference for its teaching on the MPEG-2 digital video coding standard.
The MPEG-2 standard is actually several different standards. In MPEG-2 several different profiles are defined, each corresponding to a different level of complexity of the encoded image. For each profile, different levels are defined, each level corresponding to a different image resolution. One of the MPEG-2 "standards", known as Main Profile, Main Level is intended for encoding video signals conforming to existing television standards (i.e., NTSC and PAL). Another "standard", known as Main Profile, High Level, is intended for encoding high-definition television images. Images encoded according to the Main Profile, High Level standard may have as many as 1,152 active lines per image frame and 1,920 pixels per line.
The Main Profile, Main Level standard, on the other hand, defines a maximum picture size of 768 pixels per line and 567 lines per frame. At a frame rate of 30 frames per second, signals encoded according to this standard have a data rate of 13,063,680 pixels per second. By contrast, images encoded according to the Main Profile, High Level standard have a maximum data rate of 1,152 * 1,920 * 30 or 66,355,200 pixels per second. This data rate is more than five times the data rate of image data encoded according to the Main Profile Main Level standard. The standard proposed for HDTV encoding in the United States is a subset of this standard, having as many as 1,080 lines per frame, 1,920 pixels per line and a maximum frame rate, for this frame size, of 30 frames per second. The maximum data rate for this proposed standard is still far greater than the maximum data rate for the Main Profile, Main Level standard.
In many cases, the high definition television signals having a high data rate must be filtered. Using existing techniques, however, it is difficult to implement a filter at a high data rate because current filter chips are restricted in speed. Typically, for many filter operations, the data rate of incoming video is, for example, twice the speed of a conventional filter chip, and every incoming sample must be used to generate every outgoing pixel. The data rate of the pixels produced by the filter may be the same as or greater than the data rate of the incoming pixels.
In order to process the high data rate signals, conventional filter systems may use memory in order to slow the data rate or tiling the incoming pixels to allow the filter chips to operate at a lower speed. The increased memory used by the filter, however, requires a large amount of space on an integrated circuit. Alternatively, the data samples in the high data rate signal may be estimated to produce reduced resolution images that have a lower data rate.
Thus, it is desirable to provide a filter system that operates at an elevated data rate without using extra memory for data rate reduction. It is also desirable to provide a filter system that does not reduce the resolution of the images being filtered so that the filter system may operate at a lower data rate.